The star Castor is the second brightest star in the constellation of Gemini and has long been known as a special six-star system.
Facts about Castor
The star Castor is 51 light-years away and with about 2.7 solar masses it is a blue main sequence star. In addition, its magnitude is 1.58 mag. Castor is a rare six-star system where three individual stars can be seen through the view of a telescope: Castor A, Castor B and YY Geminorum. These 3 stars are also in reality binary stars. The two brightest stars are A-class main sequence stars, which are more massive and brighter than the Sun. In addition, all three pairs of stars orbit around a common center of gravity (barycenter). To the naked eye Castor appeared as a single star and only years later was recorded as a multiple star system.